System and method for reducing desensitization of a base station transceiver for mobile wireless repeater systems

ABSTRACT

A repeater system including bi-directional amplifier circuitry that is configured for repeating signals between at least one device and a first signal source. Receiver circuitry is coupled with the amplifier circuitry provides at least one signal associated with at least one of a device or the first signal source or a second signal source. Controller circuitry is configured for monitoring a parameter of a provided signal that is reflective of a property of a signal source or a device. The monitored parameter is used to make a determination of whether repeated signals associated with the first signal source will desensitize the operation of the second signal source. The controller circuitry is also operable for adjusting the power level of the signals that are repeated by the bi-directional amplifier circuitry based on the determination that repeated signals will desensitize the operation of the second signal source.

RELATED APPLICATIONS

This Application is a non-provisional Application that claims thepriority of U.S. Provisional Patent Application No. 61/494,459, filedJun. 8, 2011 and entitled “SYSTEM AND METHOD FOR REDUCINGDESENSITIZATION OF A BASE STATION TRANSCEIVER FOR AN IN-TRAIN REPEATER”,which provisional application is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates to mobile communication systems, such as repeatersand distributed antenna systems generally and, more specifically, towireless repeater systems (repeater or distributed antenna systems) thatare used in a mobile environment, such as on a train.

BACKGROUND OF THE INVENTION

Repeaters, distributed antenna systems, and similar signal repeatingsystems are wireless communication systems that are used to extendcoverage into areas where the radio frequency (RF) signal penetrationfrom traditional base transceiver stations (BTS's) is limited or notpresent. Those low signal or no signal areas might be inside buildings,in tunnels, shadowed areas that are behind mountains, underground trainsystems, and various other isolated areas. Generally, applications forsuch repeater communication systems are for those situations where therepeater or distributed antenna system (DAS) is immobile and is mountedin a fixed location with respect to one or more base transceiverstations. In other applications, the area that has limited penetrationof the RF signals is mobile. That is, the repeater or distributedantenna system is installed in a moving or mobile environment orconveyance such as a train, ship, car, bus, or airplane, for example.

One common mobile application for repeater systems is in a train carwhere the repeater system is used to compensate for the train's signalpenetration loss. A typical train car repeater system includes a donorantenna positioned or mounted on the outside of the train car to providea radio link with a donor site, such as a nearby base transceiverstation, and a coverage antenna positioned in the interior of the traincar to provide a radio link with mobile devices located in the extendedcoverage area inside the train car. The donor and coverage antennas areconnected by a bi-directional amplifier that boosts the levels of theuplink and downlink radio signals handled by the repeater system so thatthe signals have sufficient strength to ensure that train passengers canuse smart phones and other mobile devices without dropping calls andwith the benefit of higher data rates.

Because repeater systems increase the level of uplink signals (e.g.,signals from the mobile devices to the base station) through electronicamplification, the repeater system may also generate and transmitspurious signals due to intermodulation distortion caused bynon-linearities in the bi-directional amplifier, for example. Thesespurious signal emissions, and in particular third order intermodulationproduct emissions, must be controlled to avoid interfering with othermobile communication systems. Third order intermodulation products willoften create co-channel interference in adjacent frequency bands. Thisco-channel interference will usually result in the affectedcommunication system needing a higher received signal level for theparticular desired signal than would normally be necessary in order tofunction properly. Co-channel interference therefore, effectivelydesensitizes the affected communication systems. For this reason, theallowable out-of-band spurious emissions of wireless repeater systemsare regulated by standards bodies such as the EuropeanTelecommunications Standards Institute (ETSI) and the 3^(rd) GenerationPartnership Project (3GPP) to ensure that such spurious emissions arekept below a desired level.

In a stationary environment, such a consideration takes advantage of thesomewhat static signal conditions. Interference control requirements aretypically met through proper selection of system components andconfiguration settings made at the time the repeater system iscommissioned. For example, a stationary repeater system providingextended coverage for a distant BTS may use a directional donor antennathat is oriented toward a more distant donor BTS to reduce emissions inthe direction of the nearby non-donor BTS.

However, in a mobile environment, the conditions are more dynamic. Forexample, the positions of donor and non-donor BTS's change with respectto the repeater system, as the train or other mobile platform moves.Therefore, a repeater system configuration that provides acceptableperformance at one location of a moving mobile platform may causeunacceptable interference at another location. The mobile environmentalso places additional constraints on the repeater system design, sincethe repeater system must operate under changing and somewhatunpredictable environmental conditions.

One specific issue faced by in-train repeater systems involvesdesensitization of Global System for Mobile communication—Railway(GSM-R) base stations by a mobile repeater system. GSM-R is a securesignal platform that provides voice and data communication between trainand railway communication centers. GSM-R is used by railway operatingstaff such as train drivers, engineers, dispatchers, shunting teammembers, and station controllers to provide a reliable method ofcommunication. GSM-R base stations are typically deployed along the railtrack right-of-way, so the train cars will occasionally pass within afew meters of various GSM-R base stations, as they travel on the track.In configuring such systems, GSM-R operators generally do not allowother GSM-900 service providers to co-locate base transceiver stationson the same towers or structures supporting GSM-R equipment. Therefore,when a train having an in-train repeater system passes a GSM-R basestation along a track, the donor base station that is providing GSM-900service to the riders in the train car is typically much further awayfrom the donor antenna of the repeater system than the GSM-R basestation. In a worst-case (but not uncommon) scenario, the in-trainrepeater system will be near the signal coverage edge or limit of thedonor GSM-900 base station as the train passes the GSM-R base station.Therefore, the mobile repeater system will be operating at maximumsignal gain in order to maintain signal contact with the donor basestation. In such a scenario, the uplink signals transmitted by thein-train repeater system will be much stronger at the closer GSM-R basestation than at the more distant donor base station.

This “near-far” condition for the mobile repeater system places greaterthan normal suppression requirements on the spurious emissions of anin-train repeater system. For this reason, an in-train repeater systemthat meets the suitable ETSI and 3GPP emissions standards may stillcause significant interference with or desensitization of the near GSM-Rbase station. The spurious emissions of the in-train repeater system maytherefore have to be suppressed even more than would normally berequired in other types of repeater systems to avoid interfering withthe much closer GSM-R base station. This problem is further aggravateddue to the mission-critical nature of GSM-R communications, whichincreases the importance of reducing interference, or the possibility ofinterference, with GSM-R systems caused by the mobile repeater system.

Therefore, there is a need for improved systems and methods for reducingdesensitization of certain base stations, such as GSM-R base stations,by in-train or other mobile repeater systems.

SUMMARY OF THE INVENTION

A repeater system and method in accordance with embodiments of theinvention include bi-directional amplifier circuitry that is configuredfor repeating signals between at least one device, such as a mobiledevice and a first signal source, such as a base transceiver station(BTS). Receiver circuitry is operatively coupled with the bi-directionalamplifier circuitry and is configured to receive and provide signalsfrom the mobile devices or from various signal sources, such as EGSM orGSM-R base transceiver stations. Controller circuitry that is coupledwith the receiver circuitry is configured for monitoring a parameter ofa provided signal that is reflective of a property of a signal source ora device. The signal parameter might be RSSI's from downlink signalsfrom the BTS's or may be power and frequency parameters from uplinksignals associated with a mobile device, for example. The monitoredparameters are used to make a determination of whether repeated signalsassociated with the first signal source will desensitize or adverselyaffect the operation of the second signal source. If there is adetermination that repeated signals will desensitize the operation ofthe second signal source, such as a GSM-R base transceiver station, forexample, the power level of the signals that are repeated is adjustedand more specifically reduced to avoid desensitizing the operation ofthe GSM-R base transceiver station.

In one embodiment, the RSSI value associated with a downlink signal fromthe BTS that might be affected is used and compared to a threshold todetermine if the power level should be adjusted for the repeater system.In an alternative embodiment, the RSSI values associated with downlinksignals from each of the BTS implementing the repeater and the BTS thatmight be affected are used. A difference between the two RSSI values isthen compared to a threshold to determine if the power level should beadjusted for the repeater system. In still another embodiment, theuplink signal from a mobile device is evaluated to determine if thefrequency and power level of the uplink signal indicate that certainintermodulation products of the signal will fall in the frequency bandof the BTS that might be affected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a repeater system for use in a mobile environment inaccordance with aspects of the invention.

FIG. 2 is a diagram illustrating components of an exemplary repeatersystem in accordance with an embodiment of the invention.

FIG. 2A is a diagram illustrating components of another exemplaryrepeater system in accordance with an embodiment of the invention.

FIG. 3 is a flowchart illustrating an exemplary process for reducing thecomposite output power of the repeater system in FIG. 1 in response tomeasured RSSI signals in accordance with an embodiment of the invention.

FIG. 3A is a flowchart illustrating an exemplary process for reducingthe composite output power of the repeater system in FIG. 1 in responseto measured RSSI signals in accordance with an embodiment of theinvention.

FIG. 4 graphical chart illustrating the reduction in the compositeoutput power and the effect on the desensitization of a GSM-R basestation.

DETAILED DESCRIPTION

The examples disclosed herein of an adaptive repeater system for use ina mobile environment are exemplary of the invention and do not limit thescope of the invention. One skilled in the art will recognize a varietyof applications and embodiments of the invention from the disclosureherein. Illustration and discussion are for an exemplary repeatersystem, such as a conventional repeater device, or a distributed antennasystem, or some other system that transmits, receives, and/or otherwiserepeats communication signals between a signal source (e.g., a basestation transceiver (BTS)), and mobile equipment (e.g., mobile phones,mobile computer devices, or other mobile device).

FIG. 1 shows an exemplary mobile repeater system 10 deployed in a mobileplatform, such as a moving train, that acts as part of a larger mobilecommunication network by repeating signals and facilitatingcommunication between one or more BTS's 12 belonging to a firstcommunication system, such as a GSM-900 system, and one or more mobiledevices, computers, or stations 14 that are in use in a mobile platformor moving environment, such as on a train 16. As the train moves alongits track, the repeater system 10 may also communicate with and receivedownlink signals from one or more BTS's 18 belonging to a secondcommunication system operating on frequencies different from those usedby the first BTS 12, such as a GSM-R system. Train cars and other mobilevessels used for transportation are often made of metal and other suchinsulative materials that shield the interior spaces or compartmentsfrom external RF signals. The repeater system 10 receives the downlinksignals from the first BTS 12 and rebroadcasts—or repeats—the RF signalsinside the passenger compartments of the train 16 at a level suitablefor reception by the mobile device 14 so that a user of the device mayinterface with the network.

The repeater system 10 also receives the uplink RF signals from themobile device 14 and repeats those signals outside the train 16 at alevel that allows the BTS 12 to communicate with the mobile device 14.That is, the repeater system 10 provides bi-directional communicationsbetween signal sources and the mobile devices. In a like fashion, therepeater system 10 may also repeat downlink and uplink signalsassociated with the second BTS 18, depending on whether the repeateroperator wants to enhance the coverage of the additional communicationssystem to which BTS 18 belongs. The repeater system 10 thereby extendsor improves communication system coverage in the mobile environment,such as the passenger compartments of the train 14.

FIG. 2 illustrates a diagrammatic view of an exemplary embodiment of amobile repeater system 10, as used and shown in FIG. 1. The repeatersystem 10 in FIG. 2 is in the form of a specific repeater device 10 athat has a donor antenna 30, a coverage antenna 32, and operationalelectronics 15 that couple the antennas 30, 32. In some repeater devices10 a, the electronics are contained within a unitary housing.Alternatively, the repeater system 10 of the invention might beimplemented in a distributed system, such as a distributed antennasystem (DAS) indicated specifically as system 10 b, as illustrated inFIG. 2A and discussed below. In a DAS system 10 b, the one or more donorantennas 30 are generally coupled to a main unit or master unit 21 thatis coupled to a plurality of distributed remote units or antenna units23, that are distributed throughout the mobile environment, such as inthe different compartments or cars of a train, for example. The variousremote units 23 are coupled to the master unit 21 with suitablecommunication links 25, such as coaxial or fiber-optic cables. Theinvention is described herein with respect to an embodiment where thevarious hardware components of the electronics 15 are illustrated aslocated in a common location, such as a repeater housing or housing fora master unit, but it will be understood by those of ordinary skill inthe art that the components might be distributed throughout the repeatersystem 10 as desired to implement the invention. The exemplary hardwareconfiguration is described below with respect to the embodiment of FIG.2.

The repeater system 10 includes controller circuitry 20, an input/output(I/O) interface 22, a user interface 24, memory 26, bi-directionalamplifier circuitry 28, a donor antenna 30, a coverage antenna 32, andreceiver circuitry 33, 35. The I/O interface 22 and user interface 24may provide a mechanism whereby the repeater system operator maycommunicate with and program the controller circuitry 20 and/or otherrepeater system components. The repeater system operator may therebyconfigure the repeater system 10 as desired by setting operationalparameters within the repeater system such as filter frequencies,amplifier gains, or any other parameter. The I/O interface 22 and userinterface 24 may also provide system status information and alarms tonotify the system operator of the operational status of the repeatersystem 10.

The donor antenna 30 is operatively coupled to a coverage antenna 32 bythe bi-directional amplifier circuitry 28. The bi-directional amplifiercircuitry 28 is configured for repeating signals between at least onedevice and one or more signal sources. Circuitry 28 may include one ormore duplexers 34, 36, downlink amplifier circuitry 38, uplink amplifiercircuitry 40, downlink filter circuitry 42, uplink filter circuitry 44,and a variable attenuator 46, which may be a step attenuator used toadjust the composite output power of the uplink amplifier 40. Theduplexers 34, 36 separate the downlink signal from the uplink signal,which is typically in a different frequency band from the downlinksignal. The duplexers 34, 36 thereby allow signals from a single donorantenna 30 and/or a single coverage antenna 32 to be separatelyprocessed by the bi-directional amplifier circuitry 28. In alternativeembodiments of the invention, multiple donor and coverage antennas andsignal paths may be used for handling uplink and downlink signalsseparately, in which case the duplexers 34, 36 may be omitted. Thefilter circuitry 42, 44 may include operator adjustable bandpass filtersconfigurable so that only the desired frequencies that are to berepeated pass though the bi-directional amplifier circuitry 28. Thefilter circuitry 42, 44 may thereby allow the repeater system operatorto choose which cellular carriers and signal sources may have theirsignals repeated inside the extended coverage area. Filter circuitry 42,44 may also improve the performance of the repeater system 10 byreducing transmitted noise and other interference.

The controller circuitry 20 is operatively coupled to the bi-directionalamplifier circuitry 28, and may be configured to adjust the operationalparameters of the bi-directional amplifier circuitry 28 based oninformation obtained from one or more combinations of the I/O interface22, the user interface 24, the memory 26, the bi-directional amplifiercircuitry 28, and/or the receiver circuitry 33 in accordance with theinvention. The operational parameters adjusted by the controllercircuitry 20 may include, but are not limited to, the gain of downlinkamplifier circuitry 38, the gain of uplink amplifier circuitry 40, theoperational frequencies of the filter circuitry 42, 44, and theattenuation settings of the variable attenuator 46. In accordance withaspects of the invention, the controller circuitry is operable foradjusting the power levels of the signals repeated by the amplifiercircuitry.

To provide downlink coverage inside the train 16, the donor antenna 30receives signals from one or more donor BTS's 12 or signal sources. Thedonor antenna 30 is electrically coupled to the donor side duplexer 34,which directs the downlink signals to the appropriate downlink filtercircuitry 42. The amplitude of noise and signals which are outside thedownlink frequency band of the cellular provider operating the donor BTS12 may be reduced by the downlink filter circuitry 42 so that theperformance of the downlink amplifier circuitry 38 is not adverselyaffected by out of band signals. The downlink filter circuitry 42 maythereby reduce system interference, and may also block mobile devices 14within the extended coverage area from using undesired cellular systems.The filtered signal is amplified by the downlink amplifier circuitry 38to a sufficient level to complete the downlink path, and is coupled tothe coverage antenna 32 through the coverage side duplexer 36. Thedownlink signal from the donor BTS 12 is thereby provided to theextended coverage area with sufficient power to complete the downlinkpath between the donor BTS 12 and one or more mobile devices 14.

Improved uplink coverage is provided by the repeater system 10 in asimilar manner as downlink coverage. The coverage antenna 32 receivessignals that are transmitted by the mobile devices 14. These signals areprovided to the uplink filter circuitry 44 by the coverage side duplexer36. The filtered signals pass through the variable attenuator 46 and areamplified by the uplink amplifier circuitry 40, which provides signalswith sufficient strength to the donor antenna 30 through the donor sideduplexer 34 to complete the uplink path to the donor BTS 12. As thetrain 14 travels along the track, the location of the BTS's relative therepeater system and the distance between the mobile repeater system 10and the first and second BTS's 12, 18 will change. These changes indistance will in turn cause the path loss between the BTS's 12, 18 andthe donor antenna 30 to vary as the train 14 moves.

To maintain the uplink signal levels received by the donor BTS 12 at alevel that provides a network connection of sufficient quality, themobile devices 14 in the train will typically increase their outputpower to compensate for increased path losses as the train 14 moves awayfrom the donor BTS 12. As the train 14 reaches the edge of the donor BTScoverage area, any mobile devices 14 engaged in communication with thedonor BTS 12 will typically be transmitting at their maximum outputpower. As a result of this increased mobile device output power, thecomposite power output of the uplink amplifier circuitry 40 will alsoincrease so that the repeater system 10 will typically be transmittingat its maximum rated output power in the uplink path back to the BTS 12.The increased output power demands on the uplink amplifier circuitry 40may result in increased spurious emissions by the repeater system 10.These spurious emissions may, for example, be associated with thirdorder intermodulation products generated by the interaction of multiplemobile device uplink signals with non-linearities in the uplinkamplifier circuitry 40. Thus, at the coverage edge of the GSM BTS 12,the power level of the spurious emissions of the repeater system 10,resulting from third order intermodulation products, may be at or neartheir maximum power level.

The first and second BTS's 12, 18 may be BTS's used in any number ofcommunications systems, and embodiments of the invention are not limitedto a specific type of communications system or a specific frequencyband. However, for the purposes of discussion, we will now assume aspecific example where the first BTS 12 is a donor BTS operating in theextended GSM-900 (or EGSM) frequency band, and the second BTS 18 is aBTS operating in the adjacent GSM-R frequency band user for railcommunication. In such a scenario, a repeater system 10 providingextended coverage in the EGSM band in the train will typically producethird order intermodulation products that fall into the uplink band ofthe GSM-R band, creating potential interference signals in the GSM-Rband. Thus, at the edge of the donor BTS coverage area, the repeatersystem 10 may be producing in-band GSM-R spurious signals at a maximumpower level. This may desensitize the GSM-R base station. The actuallevels and frequencies of the spurious signals will depend in part onthe linearity of the uplink amplifier circuitry 40, which is oftencharacterized by the third order intercept point, as well as the numberand frequency of uplink signals that are being transmitted.

If the second BTS 18 is sufficiently far from the repeater system 10 inthe moving train, the path loss between the donor antenna 30 and thesecond BTS 18 will usually provide sufficient attenuation of the in-bandspurious emissions to prevent desensitization of the second BTS 18.However, if the train 14 is relatively close to the second BTS 18 whilesimultaneously located at the coverage edge of the donor BTS 12, thespurious emissions incident on the second BTS 18 may be at a power levelsufficient to desensitize the receiver circuitry in the second BTS 18.Therefore, whether the repeater system is interfering with the secondBTS 18 depends on both the composite output power of the repeater 10 andthe path loss between the repeater 10 and the second BTS 18.

The output power (and thus the power level of the spurious emissions) ofthe repeater system 10 thus depends at least in part on the path lossbetween the donor antenna 30 and the first or donor BTS 12. Likewise,the resulting level of interference produced at the second BTS 18 by thespurious emissions of the repeater system 10 depends on the path lossbetween the donor antenna 30 and the second BTS 18. Therefore, inaccordance with one aspect of the invention, it has been determined thatthe amount of interference the repeater system 10 is likely producing atthe second BTS 18 can be estimated based on the path loss between thedonor antenna 30 and the first BTS 12 and the path losses between donorantenna 30 and the second BTS 18. One way to estimate the uplink pathlosses between the repeater 10 and the BTS's 12, 18 is to measure thedownlink signal strength of the BTS's 12, 18 at the repeater system 10.This downlink signal strength measurement may be provided to thecontroller circuitry 20 by the receiver circuitry 33 in the form of aparameter of the received downlink signal, such as received signalstrength indicator (RSSI).

In accordance with one aspect of the invention, the RSSI values of thevarious BTS's 12, 18 are monitored and measured. The RSSI values arethen evaluated and used to determine how the repeater system is to becontrolled to reduce the effects of any interference.

In one aspect of the invention, the difference between the monitoredlevels of the RSSI of the various BTS's is determined, and, as long asthe RSSI of the first BTS 12 providing service in the EGSM band and theRSSI of the second BTS providing service in the GSM-R band differ by anamount or value within or below a first threshold, such as 35 dB forexample, no significant desensitization will occur. That is, if thedifference between the RSSI's of the first and second BTS's 12, 18 isless than 35 dB, the path losses between the donor antenna 30 and theBTS's 12, 18 are sufficiently similar, or are close enough, so that nosignificant desensitization of the second BTS 18 will occur. Therefore,the repeater system is not significantly adjusted with respect to itsoutput power levels for the repeated signals. In accordance with anotheraspect of the invention, if the RSSI value of the GSM-R BTS (BTS 18 inthe current example) is below a second threshold, such as −30 dBm forexample, the path loss between the donor antenna 30 and the GSM-R BTS issufficient such that the repeater system will not significantlydesensitized the GSM-R BTS, even when the EGSM uplink signals are beingtransmitted at the repeater's maximum output power. Therefore, therepeater system and its output power levels will not be significantlyadjusted even if the BTS's are sufficiently apart and the BTS 12 istransmitting at maximum power. The noted first and second RSSIthresholds given in the described example will vary depending on thelinearity of the uplink amplifier 40 and other factors, such as thenumber of mobile devices transmitting. Thus, embodiments of theinvention are not limited to a particular set of RSSI measurements orvalues, determined path losses, or threshold values.

Referring now to FIGS. 3 and 4, a flow chart 50 is presentedillustrating an intelligent uplink power control method in a repeatersystem in accordance with an embodiment of the invention. Theaccompanying graphical diagram 70 illustrates exemplary relationshipsbetween: (1) the composite output power of the repeater system 10, asrepresented by plot line 72, (2) the desensitization of a GSM-R BTS by arepeater system lacking the inventive intelligent uplink power controlfeature, as represented by plot line 74, and (3) the desensitization ofthe GSM-R BTS by a repeater system including the inventive intelligentuplink power control feature, as represented by plot line 76. Theflowchart 50 is implemented as a series of steps that may generally behandled in software by controller circuitry 20 and its associatedprocessor hardware. The circuitry 15 of the invention, and specificallycontroller circuitry 20, will include one or more processors andsuitable memory (not shown) that execute software as appropriate tocontrol the operation of the repeater system 10. The processor hardwareof controller circuitry may include one or more microprocessors, digitalsignal processors, or other processing units or logic circuits toexecute software stored in memory, such as read-only-memory (ROM) orrandom access memory (RAM), or other memory to control the repeatersystem. The software and software applications or program code areexecuted to provide the functionality of the invention as describedherein.

The controller circuitry 20 monitors a parameter of a signal provided toreceive circuitry from at least one of the signal sources (BTS's) ordevice 14. The parameter is reflective of a property of the signalsource, such as the strength of the signal or the location of the sourceor path loss from the source to repeater system 10. In one embodiment,as shown in FIG. 3, in block 52, the controller circuitry 20 monitorsand obtains the RSSI values of the GSM-R and EGSM downlink signals. Thereceiver circuitry 33 provides the signal monitored by the controllercircuitry, such as the downlink signals of the BTS's. The RSSI levelsmay be provided to the controller circuitry 20 by the receiver circuitry33, which may scan the entire GSM-R and EGSM bands at a rate thatprovides an adequate response time by the controller circuitry 20 andthe intelligent uplink power control feature of the invention. To thisend, the receiver circuitry 33 may scan the GSM-R and EGSM bands every150 mS or at some other rate as appropriate.

As noted, in block 54, in one embodiment of the invention, thecontroller compares the RSSI of the GSM-R downlink signal to a firstselected threshold, which may vary depending on the characteristics ofthe repeater system, such as the repeater's third order intercept point(IP3), the maximum rated composite output power, and/or the number oftransmitting mobile devices 14 engaging the repeater system. A typicalvalue for the first selected threshold might be −30 dBm, for example. Ifthe RSSI value of the GSM-R downlink signal is below the first selectedthreshold (“Yes” branch of decision block 54) the path loss between therepeater system 10 and the GSM-R BTS 18 is considered sufficiently highsuch that the repeater system 10 will not generally desensitize theGSM-R BTS 18 with any interference signals, such as uplink signals fromthe repeater system to BTS 12, even at maximum output power levels ofthe repeater system. That is, the BTS 18 may be sufficiently far awayfrom the mobile repeater system 10 that interference desensitivity isunlikely, regardless of the location of the BTS 12 with respect to BTS18 at that time or the train position relative the BTS's. The controllercircuitry 20 will thus proceed to block 56, where the power reductionfactor is set to zero, or there is no power level reduction.

If the RSSI of the strongest GSM-R downlink signal is above the firstthreshold or greater than −30 dBm, for example, (“No” branch of decisionblock 54), the path loss between the repeater system 10 and the GSM-RBTS 18 is not sufficient or may not be sufficient to guarantee that theBTS 18 will not be desensitized by spurious emissions from the repeatersystem 10 associated with communications with BTS 12. That is, the GSM-RBTS 18 is somewhat close to the mobile repeater system 10 at that time,and thus, might be adversely affected.

In one embodiment of the invention, a reduction would occur in theoutput signal power level of repeater system 10, based only on the GSM-RRSSI value determination. Therefore, from block 54, the control flowwould proceed to block 62 through path 63 and a power reduction factorfor the repeater system would be calculated as discussed herein forreducing the power level of the repeater system. The composite outputpower for the repeater system 10 in the EGSM uplink path would then bereduced by the power reduction factor as noted in block 64.

In an alternative embodiment of the invention, after the GSM-R RSSIvalue is determined and evaluated, further conditions may be monitoredand detected to determine if the uplink output power of repeater system10 should be adjusted, even if the strongest GSM-R downlink signal isabove the first threshold (“No” in block 54). That is, other parametersof signals provided to the receiver circuitry might be monitored. Tothat end, the control flow might optionally proceed to block 58 to lookat the RSSI value differences between the RSSI's associated with the twobands. That is, receiver circuitry 33 provides downlink signals for bothBTS's 12, 18. The parameters for those signals, such as RSSI values, aremonitored. With a somewhat closely located GSM-R BTS 18 as indicated byblock 54, the repeater system may optionally evaluate at what powerlevel the repeater system and mobile devices might be transmitting. Asnoted in block 58, the controller circuitry 20 compares the monitoredRSSI value of the GSM-R downlink signal to the monitored RSSI value ofthe EGSM downlink signal. The controller circuitry then determines thedifference value or delta between those monitored or measured RSSIsignals from the BTS's 12, 18. Those RSSI signals will provide anindication of the distance of BTS 12 from repeater system 10, or othersignal conditions that might exist to indicate if the repeater system 10is operating at its maximum power relative to BTS 12 and relative to apossibly closely located GSM-R BTS 18. If the difference value betweenthe RSSI value of the GSM-R signal and the RSSI value of the EGSM signaldoes not exceed a second threshold value (“No” branch of decision block60), the output power of the repeater system does not need to beadjusted. That is, the downlink signal from the EGSM BTS 12 is strongenough relative to a close GSM-R BTS 18 that the mobile devices andrepeater system 10 will not be transmitting at their maximum power, andthus, would not likely interfere with BTS 18, even though it is closelylocated to the repeater system. The controller circuitry 20 will thusproceed to block 56, where the power reduction factor is set to zero asbefore.

If, on the other hand, the difference value or difference between theRSSI value of the GSM-R signal and the RSSI value of the EGSM signaldoes exceed the second threshold (“Yes” branch of decision block 60),the controller circuitry 20 proceeds to block 62 where the powerreduction factor is calculated for reducing the power level of therepeated signals, such as the uplink signals from repeater system 10. Atypical value for the second threshold might be about 35 dB. That is,power reduction would occur if the signal differences of the RSSI valuesexceed 35 dB. The output power level in the uplink path will then bereduced for repeater system 10, as noted in block 64.

In one embodiment of the invention, the system monitors the RSSI of theBTS's to make a determination with respect to the proximity of the BTSto the repeater system, as well as the possible output uplink power thatwould be generated by the mobile devices and repeater system based uponthat proximity. More specifically, if the RSSI value for a signal of aBTS is relatively low, such as the RSSI of the EGSM BTS 12, then anassumption is made that the BTS 12 is far enough away that mobiledevices will be broadcasting at a high level in the uplink path, andthus, create a high uplink output power from the repeater system. Such ascenario would not be a problem when the GSM-R BTS 18 is also far enoughaway from the mobile repeater system (Block 54). However, if the GSM-RBTS 18 is close to the repeater system, as indicated by the firstthreshold as illustrated in Block 54 of FIG. 3, then it may be necessaryto adjust the uplink output power as one option (proceed directly toblock 62). Alternatively, the invention would monitor other systemsignal parameters, as another option (blocks 58, 60). That is, even witha close GSM-R BTS 18, there still may not be a need to adjust the outputpower level of the repeater system 10. If the EGSM BTS 12 is also closeto the repeater system (RSSI difference between BTS's does not exceedthe second threshold), then presumably, the mobile devices will not betransmitting at their maximum power level and the uplink power level ofthe repeater system is also lower or not at a maximum power level.Therefore, the repeater uplink signals generally would not theninterfere with, or desensitize the GSM-R BTS 18. Conversely, if thedifference between the RSSI signals of those paths exceeds the secondthreshold, then presumably the more distant BTS 12 is far enough awaysuch that mobile devices and repeater system 10 may be transmitting atan uplink power level that is high enough that it may detrimentallyaffect the GSM-R BTS 18. In such a case, the uplink output power levelof the repeater system must be adjusted in accordance with theinvention. The output power level will be reduced by some powerreduction factor.

In still another alternative embodiment as illustrated in FIGS. 2 and3A, the monitored parameter is reflective of a property of the device,such as the frequency or power level of uplink signals from the device.To that end, a receiver might be added in the uplink path for detectingthe RSSI in the uplink. In FIG. 2, receiver circuitry 35 is coupled inthe uplink path of the repeater system such as to provide the RSSI's ofthe GSM-R and EGSM uplink signals to the controller circuitry 20. TheRSSI levels may be provided to the controller circuitry 20 by thereceiver circuitry 35, which may scan the entire GSM-R and EGSM bands ata rate that provides an adequate response time by the intelligent uplinkpower control feature of the invention. To this end, the receivercircuitry 35 may scan the GSM-R and EGSM bands every 150 mS. With theinformation from the receiver circuitry 35, the uplink signal powerlevel is measured and the frequencies of the uplink carriers that arereceived can be determined. The controller circuitry then determines ifthe received uplink carriers are positioned in a way and/or are at sucha power level so as to yield intermodulation products that can fall intoa GSM-R uplink band.

Turning to FIG. 3A, when the GSM-R downlink RSSI exceeds the threshold(e.g. −30 dBm) indicating a close GSM-R BTS, a determination might thenbe made regarding the power and frequency or placement of the deviceuplink signals as noted in block 84. If the uplink carriers are of ahigh enough power level and positioned in a way as to produce or presentintermodulation products in the uplink GSM-R frequency band (block 86),the power reduction factor might be implemented as noted in block 62. Ifthe carriers are positioned in a way so that no uplink intermodulationproducts would be present in the GSM-R uplink, then no power reductionis implemented (block 56).

As noted in block 62, the controller circuitry 20 determines orcalculates the power reduction factor, in accordance with the invention.The power reduction factor is calculated in one embodiment based on theRSSI of the GSM-R downlink signal and is used to adjust the compositeoutput power of the repeater system, which is represented by plot line72. As the RSSI of the GSM-R downlink increases and then exceeds aninterference threshold point, as indicated by the tests provided in FIG.3, the power reduction factor will become non-zero, so that thecomposite output power of the EGSM signals of the repeater is reduced asrepresented by line segment 78. A typical interference threshold pointmight be about −37 dBm, so that the intelligent uplink power controlwill begin reducing the composite power when the GSM-R downlink RSSIreaches about −37 dBm, and meets the other criteria, as noted in FIG. 3.Because a one dB reduction in the composite output power 72 will resultin a 3 dB reduction in the power of the third order products, the powerreduction factor may be approximated by the equation:P _(RF)=(P _(RSSI) −P _(TH))/3where P_(RF) is the power reduction factor in decibels, P_(RSSI) is theRSSI of the GSM-R downlink signal in dBm, and P_(TH) is the interferencethreshold point in dBm where the power adjustment of the inventionbegins. The power reduction factor may depend on the type of amplifiercircuitry that is implemented in the repeater system. For example, a onedB reduction might be suitable for a Class A amplifier. However,different power reduction factors might be implemented for otheramplifiers, such as amplifiers using a Feed Forward design orPre-distortion.

As illustrated by line segment 78, in some embodiments of the invention,the composite power may be reduced incrementally or in steps tofacilitate compatibility of the intelligent uplink power control featurewith digital controller circuitry 20. Embodiments using a variableattenuator 46 that is a step attenuator may round the reduction factorP_(RF) up to the nearest integer multiple of the minimum step of thestep attenuator, which may be about 1 dB. The controller circuitry 20may thereby reduce the composite output power by adjusting the variableattenuator 46 down in one dB steps for each 3 dB increase in the RSSI ofthe GSM-R downlink signal. However, in alternative embodiments of theinvention, the composite output power of the repeater system 10 may becontrolled by a continuously variable attenuator, or by any othersuitable means such as by reducing the gain of the uplink amplifiercircuitry 40.

Once the controller circuitry 20 has reduced the composite output powerof the EGSM repeater signals by the power reduction factor, thecontroller circuitry 20 will return to block 52 where the process isrepeated for continuous monitoring of potential interference scenarios.As the train moves closer to the GSM-R BTS, the RSSI of the downlinksignals received from the GSM-R BTS will increase, as shown in FIG. 4,so that the RSSI value of the signals will then exceed the interferencethreshold point P_(TH) by a greater amount. Thus, the repeater has tocontinue to adjust. In response to this increase in the RSSI of theGSM-R downlink signals, the controller circuitry 20 may increase thepower reduction factor by about 1 dB for every 3 dB increase in RSSIvalue as represented by plot line segment 78 until a maximum value forthe power reduction factor is reached. The resulting reduction in thecomposite output power of the repeater system thus, preventsdesensitization of the GSM-R BTS.

The improvement in the desensitization may be seen by the divergencebetween plot lines 74 and 76. Plot line 74 represents thedesensitization of the GSM-R BTS that occurs (for example for −40 dBmintermods) when the intelligent uplink power control feature of theinvention is not used. That is, if the plot line 72 continued at itssame level past P_(TH) indicating that the repeater system 10 wascontinuing to provide a constant composite output power, regardless ofthe RSSI level of the GSM-R downlink signal, the desensitization of theGSM-R BTS would increase, as shown in plot line 74. In contrast, plotline 76 illustrates the desensitization of the GSM-R BTS with theintelligent uplink power control feature of the invention active. As thetrain moves closer to the GSM-R BTS, the downlink RSSI value measured bythe receiver 33 may increase, but the reduction in output power of theEGSM repeater signal will maintain desensitization at a lower,manageable level. Therefore, rather than desensitization becomingsignificant, as indicated by point 80 of plot line 74, it will bemanaged and not significantly increase with increasing downlink RSSI ofthe GSM-R signal, until the output power reduction is maximized orexhausted and the repeater output level again is constant for theincreasing downlink RSSI of the GSM-R signal, as indicated by point 82of plot line 76.

Referring again to FIG. 4, where the intelligent uplink power controlfeature is active, at the point (P_(TH)) where the GSM-R BTS is about tobe desensitized by the repeater system 10, the controller circuitry 20begins reducing the composite output power level for the repeater system10, as illustrated by line segment 78. Because the interference is theresult of third order products, for every 1 dB reduction in thecomposite output power, the power level of the spurious signals willdrop about 3 dB. Thus, the reduction in the output power of the spuriousrepeater output signals will track the reduction in path loss betweenthe repeater system 10 and the GSM-R BTS (increasing GSM-R RSSI value).The level of the spurious signals at the GSM-R BTS is thus maintained ata relatively constant and reduced level just below that which mightcause desensitization of the GSM-R BTS. The desensitization of the GSM-RBTS is thus significantly reduced or eliminated by the operation of theintelligent uplink power control feature of the invention, as indicatedby plot line 76 versus plot line 74. The intelligent uplink powercontrol thereby maintains the composite output power of the repeatersystem 10 at the maximum possible level without causing desensitizationof the GSM-R BTS.

Although the RSSI value associated with the signal paths from the notedbase stations is set forth as some of the monitored parameters herein inthe disclosed example, other parameters might be monitored that arereflective of a property of one or more signal sources or a device. Forexample, other parameters might be monitored that are reflective of aproperty of the signal source that includes the proximity or closenessor location of a signal source, such as a BTS, the downlink or uplinksignal strength of signals from the signal source, and/or path lossesassociated with the signal source and the repeater system might also bemonitored in the invention. As such, the present invention and theimplementation of the intelligent uplink power control of a mobilerepeater is not limited to simply monitoring RSSI values as themonitored parameter to indicate a property of the signal sources, suchas a base station or a device, such as a mobile device. To that end,other thresholds might be developed for other signal strength indicatorsor BTS parameters that might be monitored in accordance with theinvention to determine when to activate the intelligent uplink powercontrol feature of the invention for a repeater system.

Although the disclosure herein discusses use of the invention withregard to a repeater system installed on a train, these same methods canbe applied to base stations, distributed antenna systems, and othertypes of RF transceivers and communication systems that operate inmobile environments.

While the present invention has been illustrated by the description ofthe embodiments thereof, and while the embodiments have been describedin considerable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details representative apparatusand method, and illustrative examples shown and described. Accordingly,departures may be made from such details without departure from thespirit or scope of applicant's general inventive concept.

What is claimed is:
 1. A repeater system comprising: bi-directionalamplifier circuitry configured for repeating signals between at leastone device and at least one signal source; receiver circuitry configuredfor receiving downlink signals from at least one signal source and forreceiving uplink signals from at least one device; the bi-directionalamplifier circuitry including transmitter circuitry configured fortransmitting uplink signals to at least one signal source; controllercircuitry configured for monitoring at least one parameter associatedwith a signal strength of a downlink signal from a first signal sourceand at least one parameter associated with a signal strength of adownlink signal from at least one second signal source, and alsomonitoring at least one parameter of at least one uplink signal from theat least one device and configured for controlling the transmittercircuitry of the bi-directional amplifier circuitry; the controllercircuitry further configured for using the monitored parameters,including the parameters associated with signal strength of the downlinksignals, to make a determination of whether transmitted uplink signalswill desensitize the operation of the second signal source; and thecontroller circuitry further operable for adjusting the power level ofthe transmitted uplink signals based on the determination that thoseuplink signals will desensitize the operation of the second signalsource.
 2. The repeater system of claim 1 wherein at least one monitoredparameter is reflective of a property of the signal source that includesat least one of a location of the signal source with respect to therepeater system, or a path loss between the repeater system and thesignal source or a strength of a downlink signal received from thesignal source.
 3. The repeater system of claim 1 wherein at least onemonitored parameter is an RSSI value associated with a downlink signalfrom at least one of the first and second signal sources.
 4. Therepeater system of claim 3 wherein the controller circuitry is furtherconfigured to compare the received signal strength indicator (RSSI)value to a threshold and to reduce the power level of the transmitteduplink signals in response to the RSSI value exceeding the threshold. 5.The repeater system of claim 1 wherein the receiver circuitry isconfigured for receiving downlink signals from at least the first andsecond signal sources and the controller circuitry is configured formonitoring RSSI values associated with the downlink signals from each ofthe first and second signal sources for making a determination ofwhether transmitted uplink signals will desensitize the operation of thesecond signal source.
 6. The repeater system of claim 5 wherein thecontroller circuitry is configured for determining a difference valuefor the difference between the RSSI values associated with the downlinksignals from the first and second signal sources and comparing thedifference value to a threshold, the controller circuitry adjusting thepower level of the transmitted uplink signals in response to thedifference value exceeding the threshold.
 7. The repeater system ofclaim 1 further comprising reducing the power level of the transmitteduplink signals.
 8. The repeater system of claim 1 wherein at least onemonitored parameter is reflective of a property of the device thatincludes at least one of the frequency of uplink signals from the deviceor the power level of uplink signals from the device.
 9. The repeatersystem of claim 8, wherein the controller circuitry is configured fordetermining if the frequency and power level of uplink signals from thedevice will yield intermodulation products that fall within a frequencyband of the second signal source.
 10. The repeater system of claim 1wherein the power level is adjusted by a power reduction factordetermined by the controller circuitry.
 11. The repeater system of claim1 wherein the power level is reduced incrementally.
 12. The repeatersystem of claim 1, wherein the first signal source is an EGSM signalsource and second signal source is a GSM-R signal source, the receivercircuitry configured to receive downlink signals from the first andsecond signal sources.
 13. A method of repeating signals between atleast one device and a first signal source, the method comprising:receiving uplink signals from at least one device and downlink signalsfrom at least one signal source and transmitting uplink signals to atleast one signal source; monitoring at least one parameter associatedwith a signal strength of a downlink signal from a first signal sourceand at least one parameter associated with a signal strength of adownlink signal from at least one second signal source, and alsomonitoring at least one parameter of at least one uplink signal from theat least one device; using the monitored parameters, including theparameters associated with signal strength of the downlink signals, andmaking a determination of whether transmitted uplink signals willdesensitize the operation of the second signal source; and adjusting thepower level of transmitted uplink signals based on the determinationthat those uplink signals will desensitize the operation of the secondsignal source.
 14. The method of claim 13 wherein at least one monitoredparameter is reflective of a property of the signal source that includesat least one of a location of the signal source with respect to therepeater system, or a path loss between the repeater system and thesignal source or a strength of a downlink signal received from thesignal source.
 15. The method of claim 13 further comprising monitoringa received signal strength indicator (RSSI) value associated with adownlink signal from at least one of the first and second signalsources.
 16. The method of claim 15 further comprising comparing theRSSI value to a threshold and reducing the power level of thetransmitted uplink signals in response to the RSSI value exceeding thethreshold.
 17. The method of claim 13 further comprising: receivingdownlink signals from at least the first signal source and the secondsignal source; and monitoring RSSI values associated with a the downlinksignal signals from each of the first and second signal sources andmaking a determination of whether transmitted uplink signals willdesensitize the operation of the second signal source.
 18. The method ofclaim 17 further comprising: determining a difference value for thedifference between the RSSI values associated with the downlink signalsfrom the first and second signal sources; comparing the difference valueto a threshold; and adjusting the power level of the transmitted uplinksignals in response to the difference value exceeding the threshold. 19.The method of claim 13 wherein at least one monitored parameter isreflective of a property of the device that includes at least one of thefrequency of uplink signals from the device or the power level of uplinksignals from the device, the method further comprising determining ifthe frequency and power level of uplink signals from the device willyield intermodulation products that fall within a frequency band of thesecond signal source.
 20. The method of claim 13, wherein the firstsignal source is an EGSM signal source and second signal source is aGSM-R signal source, the method further comprising receiving downlinksignals from the first and second signal sources.